Pretty weird your partition just suddenly went. It might be possible yu have a faulty hard drive which could go again at any time
I'd advise to get a replacement.
Plus since the hard drive stores all the drivers and information as well, so this could be a link to the warning if its on its way out.
So yeah, get a new one, since that shows somethings definetly up with it, having it just go for no reason
I hope this helps